Electromigration is the motion, or transport, of the atoms of an electrical conductor with time and is caused by a flow of electric current through the conductor. Many semiconductor devices include a large quantity of very small electrical conductors; and electromigration may, in certain circumstances, produce failure of these very small electrical conductors.
Electromigration tests may be utilized to test for this motion of the atoms of the electrical conductor. Historically, electromigration tests have been constant current tests in which a predetermined electric current is applied to an electromigration test structure. While such tests may be effective in certain circumstances, they may be difficult, or even impossible, to interpret in others. As an example, the presence of a defect, such as a void or a non-conductive particle, within a portion of the electromigration test structure may cause a high electric field to be developed, proximal to the defect, during constant current electromigration tests. This high electric field may, in extreme circumstances, lead to destruction of the electromigration test structure, thereby preventing the collection of meaningful electromigration data.
Historical electromigration test structures have utilized an electrically conductive diffusion barrier between the electromigration test structure and a dielectric material that surrounds the electromigration test structure. The presence of such electrically conductive diffusion barriers mitigates the impact of defects by providing an alternative electric current pathway, thus decreasing a potential for destruction of the electromigration test structure during testing thereof. However, in future technology nodes, it is anticipated that diffusion barriers may be electrically insulating, increasing a potential for destruction of the electromigration test structure during electromigration testing. Thus, there exists a need for improved systems and methods for electrically testing electromigration in an electromigration test structure.